Means for severing a thread chain



Dec. 19, 1967 c. F. MADDI ETAL 3,358,630

MEANS FOR SEVERING A THREAD CHAIN Filed Sept. 10, 1965 I60 INVENTORJ' I Chakles F. Mcddi 8. Louis N. Maddi United States Patent 3,358,630 MEANS FOR SEVERING A THREAD CHAIN Charles F. Maddi, 103 Yesu Drive, Scranton, Pa. 18505, and Louis N. Maddi, Scranton, Pa. (331 Cherry St, Dunmore, Pa. 18512) Filed Sept. 10, 1965, Ser. No. 486,277 6 Claims. (Cl. 112252) ABSTRACT OF THE DISCLOSURE A feed dog, operable through slots in a sewing machine throat plate to advance the article to be sewn, having a row of upstanding work-engaging teeth aligned with the needle hole of the sewing machine throat plate, said row of teeth having a series of teeth forming a chaining section and a second series of teeth forming a cutting section, said chaining and cutting sections being longitudinally spaced, said cutting section including at least one sharpened cutting tooth, both said series of teeth being rigidly supported on the feed dog and having their upper working edges lying substantially in the same plane.

This invention relates to a method and a means for severing a thread chain.

In the manufacture of garments, the closing of bags, and in many other instances where articles are stitched one after the other, it is the practice to pass the articles through the needle assembly of a sewing machine as fast as they can be fed to the machine by the operator without stopping or slowing the machine for each article. The successive articles thus stitched are connected by a thread chain which must be cut off the articles. The connecting thread chain may be cut oif by hand with a scissors, or by using an attachment to the needle assembly of the machine, which cuts or crushes the thread chain when an article is not in the assembly. The hand method is too slow and too imperfect for modern practice. The previous attachments have not been entirely successful because they wear very rapidly resulting in a relatively high maintenance cost as well as imperfect severing when the attachment is partially worn. In addition, the previous attachments frequently cause the materail to pucker.

A11 object of this invention is to provide a novel method for severing a thread chain.

A further object is to provide a novel means for severing a thread chain.

Another object is to provide a novel feed dog for a needle assembly which is adapted for severing a thread chain.

The novel severing means comprises, as in some previous means, a needle assembly comprising, a throat plate having a needle hole or holes therethrough, a presser foot opposite the throat plate, and a feed dog having upstanding teeth operable through slots in the throat plate to advance the articles to be sewn and the thread chain between successive articles. As used herein, the term forward refers to the direction of advance of the article to be sewn, and the phrases in front of and in back of refer to positions closer to or further from the operator. Thus, in normal operation, the articles move forward from the front to the back of the needle assembly.

The novel means includes a novel feed dog having a row of upstanding teeth aligned with the needle hole in the direction of advance of the thread chain. This row includes a plurality of blunt, non-cutting teeth in back of the needle hole for advancing the thread chain, and at least one sharp cutting tooth in back of the blunt teeth. In a preferred embodiment, the row includes a chaining section of blunt teeth in back of the needle hole, and a "ice cutting section comprised of a plurality of sharp cutting teeth in back of the chaining section. A preferred embodiment includes two additional rows of blunt non-cutting teeth, one on each side of the needle hole and parallel to the above-mentioned central row of teeth.

By the novel method, the needle assembly is operated in the normal way whereby, on each forward stroke, the feed dog advances the article between the presser foot and the throat plate. After the article passes the needle hole, a thread chain is formed and is advanced by the feed dog. While the article is present between the presser foot and the throat plate, no cutting of the thread chain oc# curs. However, when only the thread chain is present between the presser foot and the feed dog, the cutting tooth (or preferably teeth) ruptures the thread chain on each upward stroke toward the sole plate of the presser foot. In addition, the forward stroke of the feed dog (following the upward stroke) grinds the ruptured chain against the sole plate. The sharpened tooth (or teeth) does not actually actually strike the sole plate, as in previous attachments. The blunt, non-cutting teeth engage the sole plate and prevent the sharp teeth from striking the sole plate, thereby eliminating an important cause of wear which occurs in previous attachements. In the novel means, the combination of rupturing the chain during the upward stroke of the feed dog and grinding the chain dur ing the forward stroke of the feed dog severs the chain at very close intervals of the chain between successive articles. In the preferred embodiment, the side rows of blunt teeth not only advance the article but, also, help keep the sole plate aligned with the tops of the cutting teeth thereby preventing wear on both the cutting teeth and sole plate.

The invention is described below with reference to the drawing in which FIGURE 1 is a plan view of a cloth plate portion of a sewing machine having a throat plate and a feed dog arranged in accordance with one embodiment of the invention.

FIGURE 2 is a sectional view taken along line 22 of FIGURE 1 and includes a presser foot a portion of the sewing machine needle, and the sewing threads.

FIGURE 3 is a perspective of the feed dog illustrated in FIGURE 1.

In FIGURE 1, there is illustrated a portion of the work supporting cloth plate 11 of a sewing machine having a needle assembly. The cloth plate 11 is fitted with a portion of the needle assembly including a throat plate 12 secured by screws 13. The throat plate 12 is formed with spaced rectangular feed dog accommodating slots 14 and 15, one on each side of and parallel to a central row of aligned feed dog accommodating slots 16a, 16b and from front to back. Also formed in the throat plate 12 is a needle hole 17 aligned in the central row between the first and second slots 16a and 16b.

Beneath the throat plate 12 is a feed dog 22 secured by screws 21 to a feed bar 20. The feed dog 22 which is separately illustrated in FIGURE 3 is formed with continuous parallel side rows 23 and 24 of upstanding noncutting teeth, sometimes referred to as work-engaging serrations, and adapted to work upwardly through the side accommodating slots 14 and 15 respectively of the throat plate 12. Between the side rows 23 and 24 extends a web 25 supporting a central row comprised of three sections of upstanding teeth which are referred to as the feeding section 26a, the chaining section 26b, and the cutting section 260, from front to back. The sections 26a, 26b and 260 are adapted to operate upwardly through the central row of feed dog accommodating slots 16a, 16b and 160 respectively. The web 25 of the feed dog 22 has a large aperture 27 therein between the feeding and chaining sec- 25, 26a and 26b have blunt edges and are not capable of cutting or rupturing thread when the thread is pressed between the teeth and the sole plate of a presser foot in normal .operation of a sewing machine. Also, as shown in FIGURES 1, 2 and 3, the tops of all of the teeth on the feed dog are in substantially a plane so that the tops will engage the sole plate of the presser foot substantially simultaneously. With this geometry, the sharp edge of the cutting teeth 28 do not wear upon the sole plate during the operation of the needle assembly.

FIGURE 2 which is a sectional view through the throat 2 plate 12 of FIGURE 1, includes a presser foot 31 which is adapted (by a spring not shown) to press downwardly against the throat plate 12 and in opposition to the feed dog 22. The presser foot 31 has a sole plate 30 which extends over all of the teeth in the three rows on the feed dog. There is also shown a needle 32 having a short groove at one side of the needle eye and a long groove at the opposite side of the eye. FIGURE 2 also includes a representation of the sewing threads and the thread chain 33 at a time in a chaining operation when no work is present between the presser foot 31 and the throat plate 12. The thread from a conventional bobbin is indicated by BT and the thread from the needle is indicated by NT.

This invention may be applied to simple chainstitch,

lockstitch, overlock and chainlock sewing machines. In 35 such machines, the needle or needles have a simple up and down motion. The feed dog 22 partakes of conventional four motion movements; that is, an upward motion into engagement with the work or thread chain, then a forward feeding motion, then a downward motion out of engagement with the work or thread chain, and a backward returning motion to the starting position. As illustrated in FIGURE 2, the needle 33 is nearing the end of its upward f travel and the feed dog 22 has moved upward pressing the thread chain 29 against the sole plate 30. Any known feed actuating mechanism may be used to impart the desired motion to the needle 32 and the feed dog 22 provided the motions are properly timed to provide return motion to the feed dog 22 during work penetration of the needle 32.

In operation and according to the novel method, the

sewing machine is actuated and the article to be stitched is fed between the throat plate 12 and the presser foot 31. The needle 32 penetrates the article and forms a stitch.

After each stitch the article is advanced (moved forward) i by the three rows of teeth on the feed dog 22. After the article passes from between the presser foot 31 and the throat plate 12, the thread continues to chain oif and the thread chain 33 is moved forward by the action of the chaining section 2612 of the feed dog 22 on the presser foot 31. When the thread chain 33 reaches the cutting section 260, the threads comprising the thread chain 33 are cut by the sharp teeth 28 included in the cutting section 290 by the combination of rupturing the threads during the upward stroke of the feed dog and the grinding of the threads during the forward stroke of the feed dog. Since the travel of the sharp teeth 28 is limited to the travel of the feed dog 22, the sharpened teeth 28 do not grind or wear on the sole plate 30. It has been found that a greater number of sharp teeth 28 in the cutting section 260 produces a greater number of cuts through the thread chain sections between articles.

It has been found that the thread chain sometimes binds on the back wall of the back accommodating slot 160, if that back wall has a square upper corner 34. This difliculty 4 p can be avoided by rounding or beveling the corner, as

shown in FIGURE 2. What is claimed is:

1. A feed dog adapted for severing a thread chain produced on a sewing machine of the type with a throat plate having a needle hole therein, a presser foot opposite said throat plate, and slots in said throat plate to receive said feed dog for advance of the article to be sewn, said feed dog having a needle opening therein, said opening being at least as long in the direction of advance as the longest stitch which may be produced, a row of upstanding teeth aligned with said needle opening, said row being comprised, with respect to the direction of advance, of a feeding section in front of said opening, a chaining section in back of said opening, and a cutting section in back of said chaining section, said cutting section being spaced from said chaining section and having a plurality of sharp cutting teeth and the remainder of the teeth of said row being blunt and non-cutting, and all of the teeth in said row having their upper edges lying substantially in the same plane.

2. A feed dog according to claim 1, wherein is additionally provided second and third rows of upstanding, work-feeding teeth on opposite sides of said first row including the chaining and cutting sections, the upper working edges of the teeth of all three of said rows lying substantially in the same plane.

3. In a sewing machine including a throat plate having a needle hole and a plurality of feed dog accommodating slots therethrough, the combination of a feed dog, operable through said slots to advance the article to be sewn, with a presser foot sole plate having a continuous, unapertured surface portion opposed to and adapted to engage said feed dog, a row of upstanding work-engaging teeth on said feed dog aligned with said needle hole in the direction of advance of a work article, said row having a series of teeth forming a chaining section in back of said needle hole and a second series of teeth forming a cutting section in back of and substantially spaced from said chaining section, said cutting section including at least one sharp cutting tooth, both said series of teeth in the chaining and cutting sections being rigidly supported on the feed dog and having their upper working edges lying substantially in the same plane.

4. The combination according to claim 3, wherein said feed dog is provided with a second row of upstanding, work-feeding teeth on one side of said first row including the chaining and cutting sections, the upper working edges of the teeth of both of said rows lying substantially in the same plane.

5. The combination according to claim 3, wherein said feed dog is provided with second and third rows of upstanding, work-feeding teeth on opposite sides of said first row including the chaining and cutting sections, the upper working edges of the teeth of all three of said rows lying substantially in the same plane.

6. The combination according to claim 3, wherein said cutting section includes a plurality of upstanding sharp cutting teeth operable through an accommodating slot in said throat plate, the upper edge of the back wall of said latter accommodating slot being relieved to avoid binding of the thread chain thereon.

References Cited UNITED STATES PATENTS JORDON FRANKLIN, Primary Examiner.

J. R. BOLER, Assistant Examiner. 

1. A FEED DOG ADAPTED FOR SEVERING A THREAD CHAIN PRODUCED ON A SEWING MACHINE OF THE TYPE WITH A THROAT PLATE HAVING A NEEDLE HOLE THEREIN, A PRESSER FOOT OPPOSITE SAID THROAT PLATE, AND SLOTS IN SAID THROAT PLATE TO RECEIVE SAID FEED DOG FOR ADVANCE OF THE ARTICLE TO BE SEWN, SAID FEED DOG HAVING A NEEDLE OPENING THEREIN, SAID OPENING BEING AT LEAST AS LONG IN THE DIRECTION OF ADVANCE AS THE LONGEST STITCH WHICH MAY BE PRODUCED, A ROW OF UPSTANDING TEETH ALIGNED WITH SAID NEEDLE OPENING, SAID ROW BEING COMPRISED, WITH RESPECT TO THE DIRECTION OF ADVANCE, OF A FEEDING SECTION IN FRONT OF SAID OPENING, A CHAINING SECTION IN BACK OF SAID OPENING, AND A CUTTING SECTION IN BACK OF SAID CHAINING SECTION, SAID CUTTING SECTION BEING SPACED FROM SAID CHAINING SECTION AND HAVING A PLURALITY OF SHARP CUTTING TEETH AND THE REMAINDER OF THE TEETH OF SAID ROW BEING BLUNT AND NON-CUTTING, AND ALL OF THE TEETH IN SAID ROW HAVING THEIR UPPER EDGES LYING SUBSTANTIALLY IN THE SAME PLANE. 